This may help someone diagnosing connection problems with a cable modem, etc.

I connect from a router -> computer

If you go from cable modem -> computer for testing purposes, you will need to power off modem for 30 seconds.

I think I have eliminated hardware issues at this point.

Next is to see if the wireless network is setup right.

Well, if I was working on it, as a lowly home user (which I am),I'd split the problem in two. The very last thing I'd wantto throw into the mix, is having the 802.11 wirelessas a variable ( -=-=- in the diagram ). You can workon the wireless part, once you've proved Comcast isn'tripping you off. The wired portion should be more reliable.

See if the computer in question, has an option to disable thewireless portion. (My laptop, has an option to turn off theradio on the Wifi, as an example of a control.) Once the wirelessis off, and the Ethernet cable is detected running from thecomputer on the right, to the cable modem in the center,the computer should switch over to Ethernet.

If the Cable Modem includes a one port or multi-port router(modern devices are all-in-one), it likely supports DHCP anddishes out 192.168.x.x private addresses for the computersin the house.

If you can ping the cable modem from a command prompt...

ping 192.168.100.1

or use your web browser on it, that proves the wiring from theright of the diagram, to the center of the diagram is working.I got the IP address from the FAQ link below. The address to reachthe router setup page, is probably in your paper documentationsomewhere. Using a browser, you might try

The right-hand sidebar here, has a few FAQ entries for ComcastCable. There's one for signal strength, if you like to dabblein such things (that's signal strength on the Comcast cableTV wire). Or, talk to Comcast, and listen to the scripttheir tech has to offer (the ole "turn it off and turn it on"crap).

ISPs either allow users to own their own modems, or themodem is a rental. If it's a rental, it might be coveredin the FAQ. If it was purchased separately, it might havemanuals in the box, or available online, for probing it.

The modem should collect statistics. And that's one way ofdetermining whether basic operation is present or not.The status lights on the box, provide a simple go-nogostatus. But the signal level page delivered by therouter to your browser, can also give some info.

*******

I'm on ADSL, and for us as users, there is "DMT". I thinkI read somewhere, it uses telnet protocol on the local LANto talk to the ADSL box, and it downloads the stats andmakes that colorful graph. There are websites, such asdslreports, that have more info on how to interpret thenumbers in DMT. I've never run this on mine (because myADSL is in bridged mode), but I understand some peopleuse the results of such testing, to ask for a profilebump to a higher bandwidth setting.

We have to work a bit harder, if we want to debugour broken ADSL setups. But the phone company canalso wring out the line from their end, and checkparameters. It's just more reassuring to have agraph to offer as proof they're not deliveringthe level of service they should.This may help someone in the future.

If you get it working right, while using theEthernet cable, then that might point to theWifi as the busted part. But first, I'd wantto make sure the setup is rock solid overEthernet cable, before letting Comcast offthe hook in terms of delivering service. Gettingthe Wifi working, is for "bonus points".